In recent years bicycle becomes very popular and is widely used as transportation means, means for exercise and physical fitness, or leisure and sightseeing activities, either in cities or country sites. It also has been designated as one of sport contest or extreme sport items long time ago. With increasingly popularity of bicycle sports, bicycle users, whether general users, professionals or athletes, have higher demands on nearly every bicycle feature, such as maneuverability, user-friendliness of operation interface or riding comfort. To meet these requirements many types of accessories have been developed for mountain bikes or road bikes. One of them aims to improve treading efficiency of users by providing a coupling system to hold bicycle shoe and pedal together.
For instance, U.S. Pat. No. 7,225,703 discloses a bicycle pedal and crank apparatus. It mainly includes a clipless bicycle pedal and a crank arm. The clipless pedal includes a shaft, a wing, a body and a spring. The wing, body and spring are coupled on the shaft. The wing and spring are held in the body. The spring is located in the wing. The shaft has one end coupled with a sleeve fastened through a screw, and other end coupled with the crank arm through a screw ring. The screw ring holds a bearing inside. A user can latch a shoe cleat at the bottom of the bicycle shoe in the wing (or body). When the user rides the bicycle the cleat is tightly coupled with the wing, and is not easy to separate therefrom. When releasing of the cleat is desired, the cleat has to be positioned at a specific angle with the wing. Such a design allows the bicycle shoe to form a secure coupling with the pedal, hence user's stepping force can be transmitted to the crank more efficiently. Treading also is more stable.
To fabricate the aforesaid wing (or body), U.S. Pat. No. 6,851,189 discloses a method of fabrication a clipless bicycle pedal. A metal plate is stamped to form a flat inner wing and outer wing element. The wing element includes a pair of annular portions each has a spindle hole, and two ends formed respectively a tab and a groove formed in shapes complemented with each other. The wing then is bent in a rectangular structure with a plurality of bend portions. Finally the tab and groove are soldered or brazed together to become a joint.
The aforesaid conventional joining process to fabricate the wing forms a joining interface which has strength far smaller than the wing body. During the joining process a slight negligence of control parameters could result in defective joining interface. Hence when the wing receives continuous treading force of the user for a long duration, or the treading force is inadvertently greater, stress concentration is easily formed on the joining interface and results in fracture. This is especially likely to take place during contests or exercises that require high speed riding. The unstable structural strength on such a pedal system creates safety concern for the user during riding. Moreover, the aforesaid fabrication method is difficult to control structural uniformity during joining of the joining interface between the tab and groove. Production yield could drop and production cost is higher.